What is a HTTP Session?

From the time you fire the first request from a browser to a server, to the time you shut down the browser - is a single HTTP Session to this server.

All the requests the server received from this browser during this period belong to the same HTTP Session.

If you restart the browser, and send a new request to the server - that would start a new HTTP Session on the server.

If 10 (or n) people are sending requests to the server, then there are 10 (or n) simultaneous HTTP Sessions.

If you have multiple tabs open in your browser, each pointing to a different server, then you have that many HTTP Sessions open on your client side. Each server sees a single HTTP Session from you.

If you have a single tab open in your browser and send requests to multiple servers, you have that many HTTP Sessions open. Each server you sent a request to sees a single HTTP Session from you.

Note that a Login Session is different from a HTTP Session. Suppose I open a browser, login to my bank website, then logout, again login and then logout - and then shut down the browser. I had 2 Login Sessions within a single HTTP Session.

HTTP Sessions are timed out by the server if the administrator has configured an idle period timeout. Login Sessions are timed out by the application. Some internet email and news services allow you to maintain your Login Session over several days, even if you reboot your computer. HTTP Sessions will always end when you close your browser, regardless of the idle timeout set by the administrator.